Multiple cardiopulmonary diseases result in tissue hypoxia, which is a deficiency of molecular oxygen available for cellular metabolism. Tissue hypoxia may have many causes, and treatment of hypoxia is conventionally directed to the cause of the hypoxia.
When hypoxia is caused by deficiencies in the partial pressure of oxygen in inspired gas diffusing across the alveolar capillary membrane in the lung, the treatment involves increasing the partial pressure of inspired oxygen in the inspired atmosphere. Conditions such as asthma, pneumonia, and adult respiratory distress syndrome are examples of diseases which may produce tissue hypoxia because of complex pathology within the lung.
Treatment of tissue hypoxia associated with these diseases may be accomplished via multiple devices such as masks, nasal cannula, endotracheal tubes, tracheostomy tubes, mechanical ventilators and various other devices that administer oxygen. However, because of lung pathologic states such as mucosal edema, atelectasis, and bronchoconstriction, gaseous oxygen inhalation with the aforementioned devices may insufficiently treat tissue hypoxia. In addition, the inhalation of gaseous oxygen may result in oxygen toxicity and barotrauma, when excessive concentrations and gas partial pressure is used during treatment.
Tissue hypoxia may occur when blood flow to the lung is altered or decreased, thereby mismatching ventilated lung units with perfused lung units. Conditions such as primary pulmonary hypertension, and adult respiratory distress syndrome are examples of conditions which may decrease blood flow due to pulmonary artery vasoconstriction. Medications which may be administered to treat these types of lung problems may include inhalation of gaseous nitric oxide which is intended to dilate the vasculature, decrease pulmonary vascular resistance, and improve lung blood flow. Ideally, the inhalation of gaseous nitric oxide would improve the matching of ventilation with perfusion in the lung and result in improved gas exchange. However, the inhalation of nitric oxide may be associated with several complications including methemoglobinemia, rebound vasoconstriction during weaning of the gas, and hypotension. In addition, nitric oxide is an extremely expensive treatment, and may require extended periods of gas inhalation at considerable cost.